Ch 53 – Community Ecology

What is a community?

• A group of populations of different species living close enough to interact

1. Interspecific interactions

• Interspecific – between species• Can be: – Positive (+)– Negative (-)– Neutral (0)

• for each species

Interspecific competition

• Competition (-/-)• Result of resources in short supply

• http://www.youtube.com/watch?v=igkjcuw_n_U• http://www.youtube.com/watch?v=EzLADnLsNRs

• Competitive exclusion principle- – Two species competing for the same limiting resources

cannot coexist. Eventually one will have a selective advantage that will eliminate the other.

http://www.youtube.com/watch?v=rqoqfLzCN6M

Resource partitioning

• Differentiation of niches that allow similar species to coexist in a community

A. distichus perches onfence posts and othersunny surfaces.

A. insolitus usuallyperches on shadybranches.

A. ricordii

A. alinigerA. insolitus

A. distichusA. christophei

A. cybotesA. etheridgei

Niche• Ecological niche – the sum total of a species’

use of the biotic and abiotic resources in its environment

• Fundamental niche – the niche potentially occupied by a species

• Realized niche – the portion of the fundamental niche the species actually occupies

EXPERIMENT

ChthamalusBalanus

Balanusrealized niche

Chthamalusrealized niche

High tide

Low tide

High tide

Chthamalusfundamental niche

RESULTS

Ocean

For example, the presence of onebarnacle species limits the realized niche of another barnacle species

Predation

• Predator eats prey (+/-)• Predator adaptations:– Acute senses to locate and identify prey• Many have forward facing eyes & ears (i.e. fox)

– Adaptations to help catch & subdue prey:• Stingers, teeth, fangs, poisons, etc.

• http://www.youtube.com/watch?v=pNcIUIULafw

Prey defense• Cryptic coloration• camouflage

• Batesian mimicry• Unharmful mimics harmful

• Aposematic coloration• warning coloration

• Mullerian mimicry • 2 unpalatable species mimic each

other

Behavioral defenses

Herbivory

• Herbivore eats part of plant or alga (+/-)

• Animal – distinguish non-toxic from toxic plants

• Plant – defense through toxins, spines, thorns

Symbiosis• When individuals of two species live in direct

contact with each other

• Parasitism – parasite gets nourishment from host (+/-)

• Mutualism – interspecific interaction that benefits both species (+/+)

• Commensalism – benefits one species, neither helps nor harms other species (+/0)

• Symbiotic relationships – blind shrimp & goby:

• http://www.animalplanet.com/tv-shows/animal-planet-presents/videos/top-10-odd-animal-couples-shrimp-a-goby.htm

2. Communities are characterized by Diversity & trophic structure

• Species diversity – • Species richness – number of species• relative abundance – how common or rare species is

• Dominant species – have the highest biomass, or are most abundant

• Keystone species – exert strong control on community structure by their ecological roles or niches (not necessarily the most abundant)

Trophic structure

• The feeding relationships among organisms in a community

• Trophic levels – the links in the trophic structure of a community

• Food chains- what eats what

• Food webs – two or more food chains connected

3. Disturbance and community structure

• Disturbance – an event that damages a community

• Natural or human activities

• Intermediate disturbance hypothesis – • Moderate levels of disturbance create

conditions that foster greater species diversity (vs. High or Low levels of disturbance)

Ecological succession

• Transitions in species composition over ecological time

• Primary succession – • Occurs where soil has not yet formed

• Secondary succession –• Occurs where existing community cleared but soil is

intact

Mt. St. Helen’s• http://www.youtube.com/watch?v=

4RsMyVavT2Q• http://www.youtube.com/watch?v=

gQ9fV35DxLY• Yellowstone Forest Fire succession• http://www.youtube.com/watch?v=

AQQupOYonRo

4. Biogeographic factors affecting community diversity

• Two key factors:

• Latitude of community– More abundant & diverse life in tropics vs. poles

– Area of the community• Larger the geographic area of a community, the more

species

Island biogeography

• Two factors:• Size of island – the greater the size, the higher

the immigration rates, lower rates of extinction

• Distance from mainland – rate of immigration falls, extinction rates increase

• http://virtualbiologylab.org/Models/Model_IslandBioGeography.html